River's stability is all over the place, in my experience. I had a low 160's GL that was very flippy and useless into a headwind. Had a domey 169g orange Opto that was quite stable with a lot of fade, and hard to turn at all. Finally had a 165g Opto that was flat and flippier than the lightweight GL, again basically useless in the wind.
Great glide on all Rivers though, that is their main attribute. But they aren't reliable, certainly not as a 'control driver, IMO. Good for easy distance in calm conditions mainly.